1. Field of the Invention
The present invention relates to a ball screw apparatus and more particularly to a ball screw apparatus with a function of preventing dust from dispersing which is most suitable for application to devices installed in clean-rooms.
2. Discussion of the Background
A mechanism using a ball screw apparatus generally has a problem with respect to the atmospheric contamination in a clean-room as it inevitably produces iron powder dust and particles of lubricating grease due to the sliding contact between a nut and a screw shaft. The prior art ball screw apparatuses specified for such cleanrooms are lubricated with greases of low volatility and dispersion to prevent dust or oil from dispersing by vaporization. Alternatively, the device incorporating a ball screw apparatus as a whole or the moving system or feeding system thereof such as a reciprocating table is covered, and the dust is sucked in vacuum from inside of the cover.
The aforementioned measures taken in the prior art by the use of grease specified for high vacuum instead of general purpose grease, however, cannot effectively prevent dust dispersion where a high degree of cleanliness is required such as inside semiconductor manufacturing plants. Moreover, feeding characteristics are impaired by changes in lubrication to present problems in rust preventive properties or durability. The prior art means utilizing vacuum suction is defective as the reciprocating table or the feeding system as a whole should be housed in a case to thereby inconveniently increase the size of the system including the suction pump, and to increase the cost. As the cover expands/contracts, the cover produces dust by friction to further deteriorate the situation.